Electromagnetic attracted armature relays



` March 16, 1965 K. T. YEATl-:s

ELECTROMAGNETIC ATTRACTED ARMATURE RELAYS mea Jan. 15. 1960 2 Sheets-Sheet l illu FIG. 1

VALUES OFC www fw s Umml* INCREASING ARMATURE GAP FIG 2 K. T. YEATES March 16, 1965 ELECTROMAGNETIC ATTRACTED ARMATURE RELAYS Filed Jan. l5, 1960 2 Sheets-Sheet 2 United States Patent O 3,174,082 ELECTRMAGNETIC ATTRACTED ARMATURE RELAYS Kenneth Thomas Yeates, Stafford, England, assignor to The English Electric Company Limited, London, England, a British company Filed Jan. 15, 1960, Ser. No. 2,63'2 Claims priority, application Great Britain, Jan. 20, 1959, 2,089/ 59 5 Claims. (Cl. 317-156) This invention relates to electromagnetic attracted armature relays and has for its object to provide an improved relay, combining desirable relay operating features such as a high drop out ratio, a low transient overreach, and chatterless and positive operation.

According to the invention, an electromagnetic attracted armature relay of the kind having an alternating current excited operating coil with a shaded-pole magnetic system has a capacitative element connected to introduce a fixed capacitative reactance into the electrical circuit of the operating coil to modify the inductive impedance of the operating coil in dependence upon the position of the armature and thereby provide an assisting relay operating effect over the final stage of armature movement when the relay operates. The relay according to the invention includes a capacitatively-loaded secondary winding inductively coupled with the operating coil.

A feature of the invention relates to a staggered disposition of the shaded and unshaded poles of the magnet system used in conjunction with a line contact of the armature with the poles, hinge reluctance variations being swamped out by an air gap in the magnetic circuit.

Other features of the invention relate particularly to the use of the relay as a current fed device and to a method of connecting a resistor in the circuit of such a relay to provide for the adjustment of the relay setting.

The invention and its various features will now be described with reference to the accompanying drawing in which:

FIG. 1 shows a side elevation and sectional plan View of a relay embodying the invention in preferred form;

FIG. 2 shows the effect of the capacitor C in FIG. 1(5);

FIG. 3 shows a vector diagram explaining the manner in which the effect produced by the capacitor C in FIG. l(b) is obtained;

FIG. 4 shows a special circuit arrangement including the capacitor C of FIG. 1(1)); and

FIG. 5 shows an alternative circuit arrangement having an improved adjustment feature.

The relay shown in FIG. 1(a) bears a general resemblance to the conventional hinged armature relay of the Post Office type. For certain specialised applications a desirable feature of such a relay is a positive action high `drop out.

However, in a typical relay whereas the restraint force increases linearly with the armature movement the electromagnetic operating force is not linearly related to the armature movement but usually curved as indicated by the broken line in FIG. 2. There is a rapid increase in the electromagnetic attraction as the armature gap closes over its final stages. Furthermore, a very sharp decrease in electromagnetic force is found to occur over the final 0.001 inch to 0.002 inch of the armature movement. This latter decrease arises from the effect of a quadrature loop which is effective in reducing the total flux across the armature gap at a faster rate than the phase shift increases.

It has been found that with a special pole configuration this sharp decrease in the electromagnetic pull over the last 0.001 inch or so of armature travel can be elimi- 3,174,082 Patented Mar. 16, 1965 ICC nated by a suitable shaping of the poles. now be described with reference to FIG. 1.

Referring to FIG. 1(a), a hinged armature relay is shown to comprise a magnetic core structure 10 carrying an operating winding system 11 and having a hinged armature 12 which is shown in the closed position. Supported on the magnet system 10 and insulated therefrom by an insulating pillar 13 are two contact springs 14 and 1S. The upper contact spring 14 constitutes a fixed contact arm, whereas the lower contact spring 15 constitutes a movable contact arm, which is operated by the action of connecting member 16 fitted to the crank 17 of the armature 12. In the position shown in FIG. 1(a.) the armature 12 bridges the poles of the magnet system 10 and the crank 17 is moved fully in the clockwise direction to cause the connecting member 16 to urge the contacts of the contact arms together. The spring action of the contacts operates to open the armature 12 in the absence of sufficient excitation of the Winding system 11.

The feature of the construction shown in FIG. 1(a) by which the electromagnetic pull on the armature as it moves to the fully closed position is caused to increase gradually Without the sudden decrease at the end of its travel consists in the provision of a thin insulating spacer member at 18 between the upper pole of the magnet system 10 and the armature 12 and in addition the staggered configuration of the lower poles of the magnet so that the unshaded pole (the lower one in the figure) is reduced by approximately 0.001 inch. The shaded pole has a quadrature loop 19 around it as shown. This design ensures that when the armature 12 is in the closed position it does not make a flush contact with the unshaded and shaded lower poles of the magnet system 10.

In this way the relay of FIG. 101) has an operating electromagnetic force related to the armature gap corresponding to the part of the curve in FIG. 2 over which force increases with decreasing gap. As this relationship is not linear it cannot be matched readily with the linear restraining force relationship arising from the spring character of the relay system. Accordingly, a matching of the restraint and operating forces to achieve a high drop out ratio is not feasible if the full sensitivity of the relay is to be retained.

The winding system 11 of the relay is A.C. excited, and if the circumstances of this excitation are such that the current supplied to the winding system 11 is constant during the operating period of the relay the relationship between the electromagnetic force tending to close the armature and the armature gap will have the curved form already mentioned. However, if by suitable circuit connections the magnitude of the effective excitation of the winding system can be caused to vary with the armature gap it becomes possible to cause the relationship between electromagnetic operating force and armature gap to be linear and correspondingly matched to the spring effects of the restraining system. This invention provides a modification of the circuit arrangements of the excitation system of the relay which achieves this result and accordingly a relay is obtained having a high drop out ratio.

In a case in which the winding system is current excited it is found that by connecting a capacitor in effective parallel connection with the operating Winding there is a range over which the capacitor may be increased to make the relationship between the electromagnetic operating force of the relay and the armature gap substantially linear. This is illustrated by the full curves of FIG. 2 where the increasing effect of the capacitance C causes the curve to fall to a more and more linear shape.

Thus, in FIG. 1(b) a cross-sectional plan view taken This will on the line 1 1 of FIG. Ita) shows the winding system 1l to be divided into a primary winding 11a and a secondary winding 1lb. The secondary winding 11b is connected to a capacitor denoted C. The appropriate Value of the capacitance of the capacitor C can be found by experiment, one particular value being best suited to the requirement of a high drop out ratio.

The capacitance of the capacitor C in relation to the inductance of the secondary winding lib (which latter quantity is at its least when the relay armature is in its open or unattracted position and at its greatest when the latter is in its attracted or closed position) is so chosen that the ampere-turns produced in this secondary winding ilb lead the induced in this winding in the said open position, and lag behind this in the said closed position of the armature.

The total effective ampere-turns causing attraction of the armature are the vector sum of those due to the primary winding 11a and those due to the secondary winding 11b.

As will be seen from FIG. 3, the swing of the secondary ampere-turn vector from a leading to a lagging position relative to the secondary as the armature moves from the open to the closed position has the effect of reducing the length of the total ampere-turn vector, viz: of progressively reducing the total ampere-turns and hence the force exerted on the armature.

In other words, the secondary ampere-turns assist the primary ampere-turns over a rst portion of the armature travel and oppose the primary ampere-turns over a second portion thereof, whereby the modified characteristic shown in FIG. 2 is obtained.

The combination of the capacitative magnetizing circuitry wi-th the off-set pole arrangement already described is desirable because the action of the capacitor C requires a continuous unidirectional change in the characteristic curve relating torce and armature gap. The peaked portion of the broken curve shown in FIG. 2 could not be simulated easily by capacitative effects.

Owing to the close matching of the spring and pull curves made available by the arrangement shown in FG. l(b) a minimum of force difference is established between the operating electromagnetic action and the restraining spring action and this minimizes armature acceleration and so inherently gives a good transient overreach performance.

The relay described will be less sensitive to a DC. component in the A.C. input signal energising the system 11 owing yto the inclusion of the secondary circuit shown in FIG. l(b). The action of this secondary circuit if the number of turns of the windings of Ilia and 11b are equal makes the A.C. to D.C. sensitivity approximately 2. The effect of this is to improve the relay in that it is less sensitive to transient over-reach. Also, the capacitor C acts as a short-circuit to short duration DC. pulses. Thus the relay sensitivity to D.C. components in oiset current waves is considerably diminished because the Secondary winding is effectively short-circuited.

A feature of the invention provides a current operated relay which includes a resistor which is adjustable to facilitate an adjustment of the relay setting. A typical circuit suitable for this purpose is shown in FIG. 4. Here the current signal operating the relay is supplied through a current transformer having a centre-tapped secondary winding 2da. The operating winding of the relay denoted 11a as before is also centre-tapped and the secondary winding ofthe relay 11b is connected to the capacitor C as shown. A further winding 21 forms part of the primary winding of the relay system and has three times the number of turns of each half of the winding lia connected in the assisting sense. This winding 2li is connected directly between the centre tappings of the windings 11a and Zita and a resistor R which is adjustable in this case is connected across corresponding ends of the windings Ila and 26a as shown.

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The operation of the circuit shown in FIG. 4 can be understood by considering extreme values of the resistor R. If R is very high it amounts to an open circuit and the relay operating effect can be shown to be four times as great as the relay operating eiect when R is zero. In this way the resistor R can be used to provide a very sensitive adjustment of the relay setting.

In an alternative arrangement shown in FIG. 5 the winding 11a has two opposed sections 11x11 and 11(12, section M112 having more lturns than section 1101. The resistance potentiometer 3i) is connected between corresponding ends of the sections 11011 and 11512 as shown and the other ends of these sections are connected to an end connection of winding 20a and the centre tapping of winding 26a respectively, `t-he other end connection of winding 20a being connected to the tapping on the potentiometer 30.

In operation, the arrangement shown in FIG. 5 will enable a linear resistance potentiometer to be used to provide a linear range of adjustment of the relay, whereas the arrangement shown in FIG. 4 requires a variable resistor R of the non-linear type to provide a linear adjustment reference scale for the movable tapping.

What I claim as my invention and desire to secure by Letters 1Patent is:

l. An electromagnetic relay device comprising a shaded-pole magnetic system comprising a shaded pole having a quadrature loop, an operating coil circuit including a primary winding for energisation by an alternating current, a secondary winding inductively coupled to said primary winding by said magnetic system and a capacitative element connected across said secondary winding, an armature arranged for movement towards said system by attraction therebetween when said operating coil circuit is energized, a pair of electric contacts arranged for actuation as a result of said movement and spring means opposing said movement.

2. An electromagnetic relay device according to claim 1 wherein the armature is hinged to the shaded-pole magnetic system and the latter includes a nonmagnetic spacer element lat a position adjacent the armature hinge whereby the effects of magnetic reluctance variation at the hinge are substantially reduced.

3. An electromagnetic relay device comprising a shaded-pole magnetic system, an operating coil circuit including a primary winding for energisation by an alternating current, a secondary winding inductively coupled to said primary winding by said magnetic system and a capacitative element connected across said secondary winding, an armature arranged for movement towards said system by attraction therebetween when said operating coil circuit is energized, a pair of electric contacts arranged for actuation as a result of said movement and spring means opposing said movement, said primary winding having an intermediate tapping, and including an auxiliary winding, a current transformer having a primary winding `for energisation by said alternating current and a secondary winding having an intermediate tapping, and a variable impedance element for providing an adjustment for the relay setting, said auxiliary winding being connected between said intermediate tapping of said secondary winding of said current transformer Iand said intermediate tapping of said primary winding of said operating coil system, the ends of said primary winding of said operating coil system being connected to corresponding ends of the secondary winding of the current transformer and said variable impedance element being included in a said last-mentioned connection.

4. An electromagnetic relay device comprising a shaded-pole magnetic system, an operating coil circuit including a primary winding for energisation by an alternating current, a secondary winding inductively coupled to said primary winding by said magnetic system and a capacitative element connected across said secondary Winding, an armature arranged for movement towards said system by attraction therebetween when said operating coil circuit is energized, a pair of electric contacts arranged for actuation as a result of said movement and spring means opposing said movement, said operating coil system including two oppositely wound primary windings, `a current transformer having a primary winding for energisation by said alternating current and a secondary winding having :an intermediate tapping, and a potentiometerconnected variable impedance element including a variable rider for interconnecting said two oppositely wound primary windings for providing an adjustment for the relay setting, the other ends of said primary windings being respectively connected to one end and the intermediate tapping of the secondary winding of the current transformer, and the other end of the last-mentioned winding being connected to the variable rider of said impedance element.

5. An electromagnetic relay device comprising a shaded-pole magnetic system, an operating coil circuit including a primary winding for energization by an alternating current, a secondary winding inductively coupled to said primary winding by said magnetic system and a capacitative element connected across said secondary winding, `an armature arranged for movement towards said system by attraction therebetween when said operating coil circuit is energized, a pair of electric contacts arranged for actuation as a result of said movement and spring means opposing said movement, said shaded-pole magnetic system including a shaded and an unshaded pole which poles are so arranged with respect to the armature that when the armature is fully attracted to said system it makes contact with the shaded and unshaded poles over a small region of the pole faces only and leaves an air gap between itself and said pole faces which progressively decreases to zero in at least one plane.

References Cited in the file of this patent UNITED STATES PATENTS 2,282,065 Krautwig May 5, 1942 2,297,991 Senn Oct. 6, 1942 2,404,982 Owens s July 30, 1946 2,591,520 De Fligue a Apr. l, 1952 2,761,999 Warrington Sept. 4, 1956 FOREIGN PATENTS 105,293 Austria Jan. 10, 1927 950,873 France Mar. 28, 1949 

1. AN ELECTROMAGNETIC RELAY DEVICE COMPRISING A SHADED-POLE MAGNETIC SYSTEM COMPRISING A SHADED POLE HAVING A QUADRATURE LOOP, AN OPERTING COIL CIRCUIT INCLUDING A PRIMARY WINDING FOR ENERGISATION BY AN ALTERNATING CURRENT, A SECONDARY WINDING INDUCTIVELY COUPLED TO SAID PRIMARY WINDING BY SAID MAGENTIC SYSTEM AND A CAPACITATIVE ELEMENT CONNECTED ACROSS SAID SECONDARY WINDING, AN ARMATURE ARRANGED FOR MOVEMENT TOWARDS SAID SYSTEM BY ATTRACTION THEREBETWEEN WHEN SAID OPERATING COIL CIRCUIT IS ENERGIZED, A PAIR OF ELECTRIC CONTACTS 